1. Field of Use
This invention relates generally to sewerage disposal systems which include a gravity-fed wet well at a lift station and, particularly, to improved sewerage pumping apparatus for delivering sewerage from the wet well to a force main which forcibly feeds the sewerage to a sewerage treatment plant located remote from the lift station.
2. Description of the Prior Art
In one known type of sewerage disposal system, sewerage from a plurality of primary sources such as homes or dwellings is supplied by gravity through a plurality of sloped primary mains or conduits to a main collection hole or pit. Sewerage from the pit is then supplied by gravity through a sloped secondary main or conduit to a wet well which is part of a lift station. The lift station further includes sewerage pumping means which supplies sewerage from the wet well to a force main, for example, which forcibly delivers it by gravity to a collection tank at a sewerage treatment plant. Lift stations are required because a point is reached where it becomes impractical to lay gravity-flow sewer lines any deeper underground. In practice, such a known sewerage system typically comprises a plurality of pits for supplying each wet well and a plurality of wet wells for supplying each treatment plant. Also, lift stations may be provided for the force main. Furthermore, the primary mains may, for example, be up to several hundred feet in length, the secondary main up to several miles in length, and the force main up to 30 miles in length.
In such prior art sewerage systems the prior art sewerage pumping means for delivering sewerage from the wet well to the force main takes various forms. For example, sometimes electrically driven submersible pumps located in the wet well and energized from a nearby electric utility power source are used. Or, submersible pumps driven by a hydraulic motor supplied from a hydraulic pump on the surface are used. In the latter case the hydraulic pump on the surface is driven by an electric motor energized from a nearby electric utility power source. However, electric power outages, which are becoming increasingly more common and which can last anywhere from several minutes, hours or even days, interfere with operation of any submersible pump which ultimately depends on energization from the electric utility and can cause sewerage back-up and overflow from the wet well with obvious undesirable consequences in the vicinity of the lift station. One prior art solution to overcome the electric power outage problem is to provide a standby engine-driven generator at the lift station to provide emergency electric power in case of a power outage on the utility lines. However, since the electric motors to be powered by the engine-driven generator typically draw on starting up to 400 percent of the power needed for normal running, the engine-driven generator must be an oversized expensive machine which can cost more than all the rest of the equipment at the lift station. Such a machine is infrequently used and, even then, seldom at full capacity.